Embodiments of the present technique relate to a high-voltage protection system and method. Specifically, the embodiments relate to bypassing a high voltage circuit in the event of a fault.
As oil and gas fields in shallow waters are depleting, operators are tapping offshore reservoirs in deeper water with more subsea turbomachinery equipment, e.g., pumps and compressors, which are usually power intense and require the drive train comprised of electric variable speed drive (VSD) and motor. Therefore, delivery of electric power from a remote onshore utility grid or power generation on floating platform is imperative to secure reliable production and processing of oil and gas in subsea locations. Typically the transmission power is on the order of tens of megawatts for medium to large oil/gas fields.
Direct Current (DC) transmission is more efficient over longer distances than alternating current (AC) counterpart. Medium voltage (MV) or high voltage (HV) DC transmission typically requires power electronic converters which are capable of converting between HVAC and HVDC. In conventional converter topologies, each switch of the converter is designed to handle high voltages which may range from tens of kilovolts to hundreds of kilovolts depending upon the application needs. Such switches are typically arranged with series connection of multiple semiconductor devices such as insulated gate bipolar transistors (IGBTs) and thyristors. Another method is to use switches within modules of lower voltage rating and achieving the high voltages required by connecting as many modules in series as the application requires. Due to the special application in subsea, receiving-end converters need to be designed on a modular-basis which is easy to transport, marinize, install, and retrieve.
The Modular Stacked DC (MSDC) subsea power delivery architecture has been developed to transmit and distribute electric power over long tieback distance to the loads on seabed. Both sending- and receiving-end modules are connected in series; and the system is operated as a constant current source. Over-voltage will occur where the path of flowing current is open. Under fault conditions, protection of each module from over-voltage damaging requires parallel connection of protecting devices which can bypass the module in a timely fashion. Furthermore, in some instances one may need to bypass a complete DC link or part of the DC link.
Over-voltage detection is required to be fast so that protection will take place upon it effectively. For the bypass devices consisting of series-connected thyristors in MSDC, the detection delay time is expected to be less than 1 microsecond. Also, isolation from high potential components should be carefully undertaken. Usually the nominal operating voltage of bypass device in the field is higher than 10 kV. For example, it is about 11 kv between inputs of receiving-end power modules while above 30 kV in switchyard. Therefore, it poses challenge of design to meet isolation requirement.
Therefore, it is desirable to determine a method and a system that will address the foregoing issues.